<!DOCTYPE HTML>

<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>

<body>
  <script type="text/javascript">
    var w = document.documentElement.offsetWidth;
    var h = document.documentElement.offsetHeight;
    document.write(w + "<br>")
    document.write(h + "<br>")
  </script>
</body>

</html>